The present invention relates to electromagnetic interference and radiation and more specifically to systems that reduce electromagnetic radiation of printed circuit (electronic) boards.
The quest for increased performance has driven the development of electronic systems in two directions. First, there has been a dramatic increase of the level of integration that has been achieved in recent years. It is now possible to put on a single piece of semiconductor, millions of transistors running at clock frequency values expressed in hundreds of megahertz or even gigahertz for some components. Secondly, the functions to be executed are often distributed among subsystems to perform various tasks in parallel. Such a situation is typically encountered in the field of computer networks and telecommunications wherein the data are processed simultaneously in several subsystems. As a consequence of this miniaturization and high speed data transfer, electromagnetic radiation by such apparatus has increased dramatically. It is understandably necessary to properly deal with such radiation in order to prevent signals to be corrupted and to comply with international standards, such as ElectroMagnetic Compatibility (EMC).
Although there exist various means to reduce electromagnetic radiation from the surfaces of printed circuit boards (PCBs), such efforts typically fail to take the electromagnetic radiation of the board edges into account since, until recently, such radiation has been relatively negligible. However, considering the increased performance of many of today""s computer networks and telecommunications, the number of signals and corresponding transmission speeds have reached a level where edge correction is deemed necessary.
One known common approach to handling this problem involves designing the PCB to optimize placement of the PCB""s electronic devices and internal board layers. A particular rule, commonly known as the xe2x80x9c20 h rulexe2x80x9d, reduces electromagnetic radiation emitted by such board edges by a factor of about 90%. FIG. 1 represents a section of a part of a PCB 100 comprising several internal layers, including ground, voltage and signal, referred to as 110, 120 and 130 respectively. The xe2x80x9c20 h rulexe2x80x9d determines the minimum distance between the voltage layer to the closest board edge (referred to as H) as a function of the minimum distance between the ground layer to the voltage layer, referred to as h. Using this rule, the distance H must be greater or equal to 20 h. If such a design restriction reduces board edge electromagnetic radiation, it still presents several drawbacks since it is surface consuming and limited to an electromagnetic radiation threshold of about 90% (as mentioned above).
Another known solution involves surrounding the electronic board with vias connected to a ground layer, as illustrated on FIG. 2. The maximum distance between two vias (referred to as 200 in the drawing) is determined by data transmission speeds and clock frequencies. When dealing with high data transmission speeds and clock frequencies, it is necessary to closely position such vias. Understandably, such a requirement is not cost effective.
A third known approach involves metallizing the edges of the board, as illustrated on FIG. 3. Such a solution is considered efficient because it provides a continuous conductive shield (referred to as 300) of the board edges. However, such an approach is also considered relatively expensive since it requires an additional step in the manufacturing process.
It is believed, therefore, that a cost effective and relatively easy to use in manufacturing approach that effectively reduces electromagnetic radiation would constitute an advancement in the art.
It is, therefore, a primary object of the present invention to enhance the PCB art.
It is a more particular object of the invention to provide a cost effective, relatively easy to use method (and resulting product) for effectively reducing electromagnetic radiation from the edges of PCBs.
It is another object of the invention to provide such a method (and product) that is adapted to stiffen the board.
It is still another object of the invention to provide such a product that is readily adaptable for guiding, mounting and fastening the PCB within a rack or a chassis designed to accommodate same.
It is yet a further object of the invention to provide such a structure that is adapted to provide electrical contact between the PCB and the rack or chassis ground circuitry.
The accomplishment of these and other related objects is achieved by a PCB which comprises a substrate having a first edge portion and including a ground layer therein, a substantially U-shaped device secured to the PCB to provide a cover for the first edge portion, and connection means for electrically coupling the substantially U-shaped device to the ground layer within the substrate, the substantially U-shaped device substantially preventing electromagnetic radiation from being emitted from the first edge portion.
Further advantages of the present invention will become apparent to those skilled in the art upon examination of the drawings and followed detailed description.